I have HMann's 3DWorlds set, and just tried the sky dome in Poser 5, and it doesn't render black for me.

Here's a screen cap of my material settings for the sky dome. See if yours are the same.

I've noticed that sometimes, P5 screws up the material settings on items that were designed for P4. I think it has something to do with the way P4 uses 100 to mean P5's 1.